In the manufacture of sputter targets used in the semi-conductor industry, and more particularly to sputter targets used in physical vapor deposition (PVD) of thin films onto complex integrated circuits, it is desirable to produce a sputter target that will provide film uniformity, minimal particle generation during sputtering, and desired electrical properties. Furthermore, to meet the reliability requirements for diffusion barriers or plugs of complex integrated circuits, the sputter target must have high-purity and high-density.
Current methods to achieve suitable sputter targets for use in complex integrated circuits involve either hot-pressing or cold-isostatic-pressing followed by high temperature sintering. Using either of these techniques, the density of the pressed target material is about 90% of theoretical density. To obtain that 90% density, the sintering process needs to proceed at a minimum of 1800.degree. C. This high temperature results in a significant growth of the grains. Large grain size in sputter targets is deleterious to the uniformity of the deposited films. Furthermore, the sputter targets fabricated by these methods have a high oxygen content, which results in a high film electric resistivity. In addition, these processes typically involve pressing in a graphite die mold. Some volatile contaminations are contributed to the targets by this graphite mold, which results in an increase in the impurities in the films and deteriorates the reliability of the sputter devices. For example, graphite has a high alkaline element which evaporates out of the mold and is absorbed by the sputter target during pressing and sintering. Thus, the sputter targets fabricated by the hot-press or cold-isostatic-press followed by high temperature sintering have proved unreliable for use in complex integrated circuits.
There is thus a need to develop a method for fabricating high-purity, high-density tungsten sputtering targets that will meet the reliability requirements for complex integrated circuits.